1. Field of the Invention
The present invention relates to a method and an apparatus for controlling the ignition timing of internal combustion engines. The method and apparatus of the present invention are used for internal combustion engines of automotive vehicles.
2. Description of the Prior Art
In general, the ignition timing of internal combustion engines is determined based on engine running conditions, such as speed, the intake vacuum, intake air flow, and engine temperature, so as to maximize engine output power and minimize fuel consumption without causing knock. The optimal ignition timing, however, cannot easily be maintained because it varies in accordance with individual engine differences and engine ambient conditions.
A prior art method has been proposed in which knock is sensed by a device which detects engine vibration at the detonation stroke. In this method, the ignition timing is retarded to a predetermined period upon knock and is advanced by a predetermined rate otherwise. This works to suppress knock below a predetermined level.
This prior art method, however, has a problem. When correcting the ignition timing by a predetermined rate, large amounts of correction cause large variations in ignition timing near the optimum state, though also resulting in a fast speed of approach to the approximate optimum state. This results in large variation of engine torque and, hence, reduced engine drivability. Contrary to this, small amounts of correction result in a low speed of approach to the approximate optimum state, though also causing less variations in ignition timing near the optimum state. This results in continued failure to meet the optimum ignition timing, hence, confined loss of output power.